At present, in optical fiber telecommunications, access networks are known in which a given central unit is connected to a remote unit situated at the premises of a given customer. That type of technology is known as “point to point” in contrast to “point-to-multipoint” technology in which a central unit can be connected on its customer side to a plurality of remote units. Although the invention preferably relates to point-to-point transmission, it can also be applied in the context of point-to-multi-point transmission, in particular passive optical network (PON) type transmission.
The communication mode that is used most commonly in point-to-point technology is simultaneous communication mode, also known as “simplex” mode which makes use of one optical fiber for each transmission direction.
Until now, telecommunications operators, in particular those using optical fibers, have had control over both ends of the transmission link, i.e. the central unit and the remote unit, and both units were installed or withdrawn simultaneously. For operators this situation implied a degree of technological stability and inalienable rights over their customers and their units.
Nowadays, the context in which operators operate has been changed considerably because of the changes that have taken place in optoelectronic component technology, because of the introduction of competition on the optical fiber telecommunications market, and because of the appearance of new techniques such as wavelength division multiplexing (WDM). In outline, WDM differs from the techniques previously used on optical fiber access networks in that known techniques presently in use implement one or two wavelengths selected in spectral windows centered around 1.3 μm or 1.5 μm between the central unit and all of the remote customer units, with the optoelectronic components in the various units being of the broadband type, whereas with the WDM technique at least the window at the central unit, preferably around 1.5 μm, is subdivided into a plurality of carrier wavelengths, each being allocated to a particular remote unit. For example, in dense wavelength division multiplexing (DWDM), the window around 1.5 μm which extends from 1.48 μm to 1.58 μm is subdivided into 64 carrier wavelength channels. In practice, each remote unit can be provided with a filter centered on the channel that is allocated thereto while the central unit has one or more tunable lasers suitable for emitting at each carrier wavelength.
A consequence of this new situation has been to oblige operators to provide for a degree of interoperability between their own central units and the remote units of their customers. This interoperability also presents numerous advantages in particular since it makes it possible to lower the price of components by putting manufacturers into competition and it makes it possible to diversify sources of supply. Furthermore, interoperability makes it easier to introduce new techniques such as WDM. Finally, because of the independence that is obtained between units, the operator is no longer responsible for day-to-day management of all of the units at both ends of the link nor is there any need to maintain consistency when replacing some of the units only.
Nevertheless, interoperability assumes that central units and remote units can be connected independently of the identities of the manufacturers and of their particular design decisions. Unfortunately, although an operator remains in charge of central units, the operator's knowledge about remote units that are to be connected to the network is not necessarily completely reliable, particularly as concerns their communication modes.